The giant Oklahoma Apatosaurus: OMNH 1670

April 25, 2012

Something I’ve always intended to do but never gotten around to is posting on some of the immense Apatosaurus elements from the Oklahoma panhandle. Here’s one of the most impressive, OMNH 1670, an isolated dorsal. Notice that the tip of the neural spine is ever-so-shallowly bifurcated, which in Apatosaurus indicates a D4, D5, or D6. The low parapophyses and fat transverse processes are similar to D4, but Apatosaurus D4s usually have somewhat broader spines, so I’m guessing this thing is a D5. These things vary and I could easily be off by a position in either direction.

Next to it is D5 of CM 3018, the holotype specimen of Apatosaurus louisae (from Gilmore 1936: plate 25), which has served as the basis for many of the published mass estimates of the genus Apatosaurus. OMNH 1670 is 135 cm tall, compared to 106 cm for D5 of CM 3018. If the rest of the animal scaled the same way, it would have been 1.27^3 = 2 times as massive. Mass estimates for CM 3018 are all over the map, from about 18 tons up to roughly twice that, so the big Oklahoma Apatosaurus was probably in Supersaurus territory, mass-wise, and may have rivaled some of the big titanosaurs (Update: see the two giant diplodocids square off in a cool follow-up post by Supersaurus wrangler Scott Hartman). Here’s a fun rainy-day activity: take any skeletal reconstruction of Apatosaurus, clone it in Photoshop or GIMP, scale it up by 27%, and park it next to the original. It looks a lot bigger. So I’m continually surprised that Apatosaurus is so rarely mentioned in the various roundups of giant sauropods, both in the technical literature and in popular articles online. This vertebra was figured by Stovall (1938)–if I get inspired, I’ll dig up that figure and post it another day (hey, look, I did!).

Fun fact: in Apatosaurus the tallest (most posterior) dorsals are 1.3-1.5 times as tall as D5 (Gilmore 1936: 201). So D10 from this individual was probably between 1.7 and 2 meters tall–not quite in Amphicoelias fragillimus territory but getting closer than I’ll bet most people suspected.

NB: if you try to use the scale bar lying on the centrum of OMNH 1670 to check my numbers, you will get a wonky answer. The problem is that the vertebra is so large that it is almost impossible to get far enough back from it (above it, in this case, since it is lying on a padded pallet) to get a shot free from distortion due to parallax. For this shot, the pallet with the vert was on the floor, and I was standing on top of the tallest ladder in the OMNH collections, leaning out over the vert to get centered over the prezygapophyses, and shooting straight down–in other words, I had done everything possible to minimize the visual distortion. But it still crept in. Anyway, trust the measurements, which I–and presumably Gilmore–made with a good old reliable tape measure.

References

Gilmore, C.W. 1936. Osteology of Apatosaurus with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11:175-300.

Stovall, J.W. 1938. The Morrison of Oklahoma and its dinosaurs. Journal of Geology 46:583-600.

Darn it, Steve, you’re using up stuff I was going to talk about later! :-) Good catch. Yeah, the centrum is mostly sculpture. If you click through to the hi-rez version, you can see the transition from real bone, which is bumpy and lighter in color, to the plaster, which is smoother and slightly darker.

I have a sketch in one of my notebooks that shows which parts of this vert are real and which ain’t. I should do another post with Stovall’s figure and that sketch.

(What I should really do is scan all of my notebooks. Then all that data would be backed up, more easily accessible, and more easily mined for future SV-POW! posts.)

Great! Could it be a new Apatosaurus species, due to it’s larger size?

I would be very reluctant to argue that it’s a new species based on size alone. For one thing, as discussed in this post, essentially ALL of the big mounted sauropod skeletons have some unfused bits, indicating that perhaps they weren’t done growing. For another, most tetrapods show a wide range of adult body sizes. Even leaving aside humans, for which we have a larger-than-normal sample size, it’s not unusual to find adult tetrapods of the same species that differ in mass by a factor of two or more, which is the same magnitude of difference involved here.

That’s not to say that the Oklahoma Apato isn’t a new species, either. There is a LOT of Morrison sauropod material in the OMNH collections and very little of it has been systematically studied, let alone published on. It is entirely possible that new characters or new combinations of characters lurk in that material. Sounds like a great thesis…for someone else. ;-)

Heh. Who knows? It’s pretty clearly Apatosaurus, but which existing species it belongs to, if it belongs to any of them, will require (1) going through all the material and documenting the relevant characters, and (2) doing a phylogenetic analysis. The second part shouldn’t be too bad, since there is an existing specimen-level phylogeny for Apatosaurus to build on–that of Upchurch et al. 2005 (we badly need such an analysis for Diplodocus and Camarasaurus, too). But the first part would be a mountain of work that I am not well prepared for, either geographically or by inclination. It really calls out for someone who is willing to live in collections for a few months. I used to be that guy, in that museum, but I had other fish to fry (namely this one and this one). Hopefully some ambitious OU grad student will take this on at some point.

It would almost have to be, if it’s ~30% bigger than CM 3018 in linear terms.

And is the skull on its mount made from the animal’s original bones(mandible, braincase, etc.) or just a reconstruction?

There are Apatosaurus skull pieces from the same quarry, but nothing like a complete skull. The skull, like most of the mounted skeleton, is a reconstruction. OMNH 1670 is just one of several very large elements pointing to the existence of at least two very large Apatosaurus individuals from the Kenton quarries, but the material is nowhere near complete.

BTW, have scientists already found some pieces of Barosaurus lentus skull(braincase, dentaries, nasals, etc.)? I was wondering if Barosaurus is the sister genus of Diplodocus, would they have an almost identical skull morphology. Also, did Apatosaurus excelsus and Apatosaurus ajax overlapped (at least partially) in their temporal range and if not, which is the older species.

Not that I know of. McIntosh (2005:44) wrote: “The skull and mandible have not been recovered with any Barosaurus specimens in North America. It is possible that some of the skull materials referred to Diplodocus actually belong to this taxon, but this possibility will be explored elsewhere.” The only newly recognised Barosaurus material that I know of since then is the ROM specimen, which hasn’t been formally described. But from the ROM’s press release it doesn’t seem that any skull material is included.

I was wondering if Barosaurus is the sister genus of Diplodocus, would they have an almost identical skull morphology.

They are indeed sister taxa in every published phylogenetic analysis that includes both — including that of Whitlock (2011), which includes the porposed diplodocines Tornieria and Australodocus. So there is every reason to expect that their skulls would be very similar — especially bearing in mind how similar the skull of the more distantly related Apatosaurus is.

Also, did Apatosaurus excelsus and Apatosaurus ajax overlapped (at least partially) in their temporal range and if not, which is the older species.

Overlapped. The type specimens are both from quarries in the Brushy Basin Member of the Morrison Fonmation. But I don’t know the ages of referred specimens, so the overlap may not be total. Matt?

Sorry if I post questions here by segments. I am just starting to take interest in sauropods after the TAST (Torosaurus as senescent Triceratops) hypothesis came out…I am also wonderingif Barosaurus and Diplodocus overlapped in their temporal range and which of the two genera is older….

Regarding Barosaurus skulls, there is a dissertation online about the taphonomy of the Howe Quarry by Ioannis Michalis.
He notes that most of the specimens found there are Barosaurus.
There is a chart showing the different type of elements found in the quarry, and it lists ten skulls; seven were apparently found loose and three associated with juvenile Barosaurus skeletons.

I’ve never seen the Eobrontosaurus material or even read the paper in more than a very superficial scan, so I have no opinion worth knowing. I can tell you that people I respect have reached very different conclusions about it.

[…] it ended up being generically synonymised with (see the sacra of the two taxa compared below). The giant Oklahoma Apatosaurus is about 1.4 times the size of A. louisae CM 3018 in most linear measures, but some of the neural […]